This invention relates in general to rollers, for example for use in fuser assemblies of reproduction apparatus, and more particularly to construction of fuser, pressure, or heater rollers capable of operating at elevated temperatures.
In reproduction apparatus, such as copier/duplicators and printers for example, fuser rollers or heated rollers are commonly used which include two end caps, which can be made from stainless steel, that are joined to a thermally conductive tube such as aluminum or coppers or alloys of these two materials. There are many known methods for joining the end caps to the tube, such as mechanically bolting, press fit, retaining rings, welding etc. If the end caps and tube are made from the same material, forming techniques such as spinning and swagging can be employed where joining techniques are not required.
Due to its low cost, one of the most commonly methods for joining end caps to tubing is by friction welding. Friction welding consists of either inertia or direct drive friction welding. If the end cap and the tube include materials that are weldable, than a butt type weld design can be used (see EP 0 395 385 published Nov. 31, 1990). If the end cap and the tube include materials that are not readily weldable, than an open dovetail weld design can be used (see U.S. Pat. No. 5,094,613).
The major reasons for the use of prior art open dovetail weld design in joining end caps to tubing (as shown in FIG. 1) is that under prior operating conditions it was found to result in formation of an excellent joint. It is believed that this was due to the fact that during welding the tube material (typically aluminum) is forged into the dovetail during friction welding at a forging temperature of approximately 900xc2x0 F. to 1100xc2x0 F. This results in an effective shrink fit. The dovetail configuration then prevents the gudgeon from walking out during operation at prior normal operating temperatures. Furthermore, depending on the materials selected and the friction weld parameters, some surface welding may occur between the two materials at the weld joint to enhance the joint bond.
It has been found, however, that under severe stress conditions, an open dovetail design could result in joint failure if the stresses exceed the yield point of the materials being used. One major component of these stresses is the loading imparted along the length of the roller. Another major component of these stresses is as a result of the differential coefficient of thermal expansion of the two materials from room temperature to fusing core operating temperature. The higher the operating temperature of the fuser roll, the higher the stresses created at the joint due to the differential rates of material expansion.
The two materials most commonly used for rollers of a reproduction apparatus fuser assembly are aluminum for the tube and stainless steel for the gudgeon. With the open dovetail design, at fusing temperature, the aluminum wants to grow away from the gudgeon. As long as material does not yield or fatigue, the weld joint should last forever. For fuser roll cores, where the operating temperature is held under 400xc2x0 F., the open dovetail design works very well. However, in order to provide satisfactory controllable fusing, particularly with modem color reproduction apparatus, the fuser assembly operating temperatures may exceed 400xc2x0 F., and extend to approximately 750xc2x0 F. At such elevated operating temperatures, the aluminum of the tube will start to creep because it has a very low creep strength. Accordingly, the shrink fit will be reduced or completely lost thereby resulting joint failure.
In view of the above, this invention is directed to a reproduction apparatus fuser assembly roller construction (operable in an environment of between 400xc2x0 F. and 750xc2x0 F.) whereby a tube is connected to an end gudgeon in a manner which substantially prevents separation of the roller and end gudgeon. The roller includes a generally elongated substantially cylindrical tube. End gudgeons are provided for sealing the ends of the cylindrical tube. Each of the end gudgeons is respectively associated with an end of the cylindrical tube such that after a weld joint is formed between the cylindrical tube and the end gudgeon, the end gudgeon provides a compression joint to prevent the cylindrical tube from separating from the end gudgeon, due to material creep, at elevated operating temperatures.
The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiment presented below.